The electron transport chain takes place on the inner mitochondrial membrane in eukaryotic cells, and in the plasma membrane of prokaryotes.

In more detail for eukaryotes:

  • The electron transport chain (ETC) complexes are embedded in the inner membrane of the mitochondrion.
  • Protons are pumped from the mitochondrial matrix across this inner membrane into the intermembrane space, creating the gradient that drives ATP synthase.

For prokaryotes (which do not have mitochondria):

  • Their ETC is located in the cell’s plasma membrane, using that membrane to create a proton gradient in a similar way.